thumbor

Thumbor is an on-demand image processing server that handles cropping, resizing, and transformations via URL parameters. Point it at your image storage, construct a URL with the dimensions and filters you want, and it delivers the processed image. Wikipedia, Forbes, and Square all run it in production.

Runs as a Python service with optional face detection (using OpenCV) and smart cropping powered by AI. You will need a storage backend (S3, filesystem, or others via plugins) and a caching layer for performance. Not a one-click install, but the architecture is clean and well-documented.

Free for everyone, no restrictions. Solo devs can spin it up for a side project. Teams with heavy image traffic should pair it with a CDN and proper caching. At scale, the ops burden is mostly about tuning workers and cache invalidation.

The catch: you are running and maintaining an image processing pipeline yourself. If you would rather not think about scaling image workers, Cloudinary or Imgix handles all of that for a monthly fee.